Using the areal unit segregation measure to identify racially “packed” and “cracked” legislative districts

Abstract

This paper provides a novel and systematic technique for differentiating legislative districts that are “naturally packed” with racial minorities from those that are “unnaturally packed.” Unnaturally packed districts—called segregated districts in this paper—contain greater shares of racial minorities than the share of racial minorities in the geographic regions in which they are located. By contrast, “naturally packed” districts are the ineluctable result of the geographic concentration of large numbers of minorities (often in urban areas) and are thus non-segregated. Differentiating segregated from non-segregated districts requires observing the average share of racial minorities among the nearest N neighbors of a district’s residents (where N is the number of people in a state divided by the number of legislative districts). When the share of minorities in a district exceeds the average share of minorities who are the nearest N neighbors of district residents, the district is segregated. This paper explains how to measure segregation for individual legislative districts, provides a test case by examining Virginia’s State House Districts ruled Unconstitutional in Bethune-Hill v. Virginia Board of Elections, and shows how measuring segregation provides information different from typical ways of detecting gerrymanders.